Electronic Applications: Part Two

Sommario:

Magnet wire of aluminum is a relatively new product; it utilizes EC aluminum. Its cross-sectional area must be 1.6 times that of copper wire to achieve equal direct-current resistance. Although this is a disadvantage in coils where space is a major consideration, aluminum wire has several economic advantages that often outweigh space considerations.
Aluminum conductor weighs half as much as equivalent copper conductor. The lighter weight is attractive for small transformers, coils, motors, and portable equipment, especially in aerospace applications where reduced component weight allows a highly important increase in payload.

Magnet Conductors

Magnet wire of aluminum is a relatively new product; it utilizes EC aluminum. Its cross-sectional area must be 1.6 times that of copper wire to achieve equal direct-current resistance. Although this is a disadvantage in coils where space is a major consideration, aluminum wire has several economic advantages that often outweigh space considerations.

Aluminum conductor weighs half as much as equivalent copper conductor. The lighter weight is attractive for small transformers, coils, motors, and portable equipment, especially in aerospace applications where reduced component weight allows a highly important increase in payload.

The lower mass of aluminum-wound coils results in lower inertia, improving the performance of a wide variety of equipment. Low mass simplifies dynamic balancing of rotary equipment. It also results in higher sensitivity and response in many coil applications, as in instruments and acoustical devices. Many classes of motors can be redesigned readily to utilize aluminum magnet wire.

Magnet Strip. With the development of aluminum strip conductors during the last decade, a new concept in electromagnetic coil design and winding technique has been exploited. Strip conductor coils can be wound with higher space factors and less layer-to-layer insulation than coils wound with round wire. With proper selection of strip insulation and coil design, it is possible to produce an aluminum strip-wound coil having the same physical dimensions and electrical characteristics as a coil wound with round copper conductor. The finished aluminum coil may weigh only half as much as the equivalent copper wire coil. Perhaps the most significant advantage of the aluminum strip-wound coil is cost.

Generating Systems Equipment

Electrical Applications. Isolated-phase bus is the most widely accepted method for connecting generators to transformers. Aluminum bus is cheaper than copper, and easier to handle and install. Because aluminum conductors are welded easily in the factory or field, the number of bolted joints needed to install isolated-phase bus systems is reduced significantly.

Aluminum is used widely for high-voltage switchyard bus, as tubular aluminum conductors provide a very favorable combination of mechanical and electrical characteristics.

Mechanical Applications. Aluminum’s resistance to corrosion contributes major economies in condensate storage tanks, because no maintenance is required inside or outside and no iron is introduced into the boilers. Other applications of aluminum include control tubing,-tanks, covers, boiler lagging, jacketing, panels, and canopies.

Power Utilization and Conversion Equipment

Motors. The majority of squirrel cage induction motors employ an integrally cast aluminum rotor. This incorporates the conductor bars, end rings and cooling fan, eliminating welding or brazing and minimizing the use of bolts, screws and other pieces typical of assembly. Heat transfer from the conductor bars to the sheet steel laminations is excellent, minimizing local overheating within the rotor during a severe overload peak.

The choice of alloy for the rotors depends largely on the operating characteristics of the motor. A particular rotor design may require an aluminum alloy having a high, low or intermediate conductivity. Values for rotor alloys range from 60.5% iacs for a high-conductivity type to 23% for 380-F.

Rectifiers. The major applications of aluminum in rectifier equipment are electrical conductors, heat sinks, and enclosures.

Aluminum offers several advantages that explain its frequent selection as a heat-sink material, even though its volume thermal conductivity is less than that of copper. The extrudability of aluminum permits versatility in the design of aluminum heat sinks with extended surfaces. Configurations ideal for heat dissipation can be produced economically. Extruded sections, usually of 6xxx series alloys, can be color anodized to increase the emissivity of the radiating surfaces, where required by design or service conditions. An extruded aluminum section often functions both as a heat sink and an electrical conductor.

Communications and Electronics Equipment

Antennas. Aluminum is utilized extensively in radar and microwave antennas for air-borne and naval electronic equipment, primarily because of its high strength-to-weight ratio and the rigidity resulting from the large sections permitted. Structural shapes and large-diameter pipe and tube are used in the supporting structures. Parabolic reflectors, spun from alloy 1100 sheet, are supported by a frame of extruded or structural shapes, or pipe. Castings are common for corners, bases and covers.

Virtually all outdoor television antennas are constructed of drawn or welded aluminum tube, usually in 3003 or 6063 alloy. Aluminum dominates this application because of its combination of light weight, electrical conductivity and resistance to weathering.

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